/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.event;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;
import org.springframework.util.ErrorHandler;

import java.util.concurrent.Executor;

/**
 * Simple implementation of the {@link ApplicationEventMulticaster} interface.
 * <p>
 * Multicasts all events to all registered listeners, leaving it up to
 * the listeners to ignore events that they are not interested in.
 * Listeners will usually perform corresponding {@code instanceof}
 * checks on the passed-in event object.
 * <p>
 * By default, all listeners are invoked in the calling thread.
 * This allows the danger of a rogue listener blocking the entire application,
 * but adds minimal overhead. Specify an alternative task executor to have
 * listeners executed in different threads, for example from a thread pool.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Stephane Nicoll
 * @see #setTaskExecutor
 */
public class SimpleApplicationEventMulticaster extends AbstractApplicationEventMulticaster {
    @Nullable
    private Executor taskExecutor;

    @Nullable
    private ErrorHandler errorHandler;

    /**
     * Create a new SimpleApplicationEventMulticaster.
     */
    public SimpleApplicationEventMulticaster() {
    }

    /**
     * Create a new SimpleApplicationEventMulticaster for the given BeanFactory.
     */
    public SimpleApplicationEventMulticaster(BeanFactory beanFactory) {
        setBeanFactory(beanFactory);
    }

    /**
     * Set a custom executor (typically a {@link org.springframework.core.task.TaskExecutor})
     * to invoke each listener with.
     * <p>
     * Default is equivalent to {@link org.springframework.core.task.SyncTaskExecutor},
     * executing all listeners synchronously in the calling thread.
     * <p>
     * Consider specifying an asynchronous task executor here to not block the
     * caller until all listeners have been executed. However, note that asynchronous
     * execution will not participate in the caller's thread context (class loader,
     * transaction association) unless the TaskExecutor explicitly supports this.
     *
     * @see org.springframework.core.task.SyncTaskExecutor
     * @see org.springframework.core.task.SimpleAsyncTaskExecutor
     */
    public void setTaskExecutor(@Nullable Executor taskExecutor) {
        this.taskExecutor = taskExecutor;
    }

    /**
     * Return the current task executor for this multicaster.
     */
    @Nullable
    protected Executor getTaskExecutor() {
        return this.taskExecutor;
    }

    /**
     * Set the {@link ErrorHandler} to invoke in case an exception is thrown
     * from a listener.
     * <p>
     * Default is none, with a listener exception stopping the current
     * multicast and getting propagated to the publisher of the current event.
     * If a {@linkplain #setTaskExecutor task executor} is specified, each
     * individual listener exception will get propagated to the executor but
     * won't necessarily stop execution of other listeners.
     * <p>
     * Consider setting an {@link ErrorHandler} implementation that catches
     * and logs exceptions (a la
     * {@link org.springframework.scheduling.support.TaskUtils#LOG_AND_SUPPRESS_ERROR_HANDLER})
     * or an implementation that logs exceptions while nevertheless propagating them
     * (e.g. {@link org.springframework.scheduling.support.TaskUtils#LOG_AND_PROPAGATE_ERROR_HANDLER}).
     *
     * @since 4.1
     */
    public void setErrorHandler(@Nullable ErrorHandler errorHandler) {
        this.errorHandler = errorHandler;
    }

    /**
     * Return the current error handler for this multicaster.
     *
     * @since 4.1
     */
    @Nullable
    protected ErrorHandler getErrorHandler() {
        return this.errorHandler;
    }

    @Override
    public void multicastEvent(ApplicationEvent event) {
        multicastEvent(event, resolveDefaultEventType(event));
    }

    @Override
    public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
        ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        // 遍历容器中定义的所有事件监听器
        for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
            Executor executor = getTaskExecutor();
            if (executor != null) {
                // 异步调用事件监听器
                executor.execute(() -> invokeListener(listener, event));
            } else {
                // 调用事件监听器
                invokeListener(listener, event);
            }
        }
    }

    private ResolvableType resolveDefaultEventType(ApplicationEvent event) {
        return ResolvableType.forInstance(event);
    }

    /**
     * Invoke the given listener with the given event.
     *
     * @param listener the ApplicationListener to invoke
     * @param event    the current event to propagate
     * @since 4.1
     */
    protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
        ErrorHandler errorHandler = getErrorHandler();
        if (errorHandler != null) {
            try {
                doInvokeListener(listener, event);
            } catch (Throwable err) {
                errorHandler.handleError(err);
            }
        } else {
            doInvokeListener(listener, event);
        }
    }

    @SuppressWarnings({"unchecked", "rawtypes"})
    private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
        try {
            // 处理监听器监听到的事件
            listener.onApplicationEvent(event);
        } catch (ClassCastException ex) {
            String msg = ex.getMessage();
            if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
                // Possibly a lambda-defined listener which we could not resolve the generic event type for
                // -> let's suppress the exception and just log a debug message.
                Log logger = LogFactory.getLog(getClass());
                if (logger.isDebugEnabled()) {
                    logger.debug("Non-matching event type for listener: " + listener, ex);
                }
            } else {
                throw ex;
            }
        }
    }

    private boolean matchesClassCastMessage(String classCastMessage, Class<?> eventClass) {
        // On Java 8, the message starts with the class name: "java.lang.String cannot be cast..."
        if (classCastMessage.startsWith(eventClass.getName())) {
            return true;
        }
        // On Java 11, the message starts with "class ..." a.k.a. Class.toString()
        if (classCastMessage.startsWith(eventClass.toString())) {
            return true;
        }
        // On Java 9, the message used to contain the module name: "java.base/java.lang.String cannot be cast..."
        int moduleSeparatorIndex = classCastMessage.indexOf('/');
        if (moduleSeparatorIndex != -1 && classCastMessage.startsWith(eventClass.getName(), moduleSeparatorIndex + 1)) {
            return true;
        }
        // Assuming an unrelated class cast failure...
        return false;
    }
}
